spi: spi-qcom-geni: Clear the RX fifo if FIFO has data after timeout

Dummy read the rx fifo in case RX fifo has data after a timeout. This
is to clear the spurious rx watermark interrupt that keeps firing due
to stale data in the rx fifo.

Change-Id: I4094261e00d61b07cd53a7ae508efdad73c3f022
Signed-off-by: Vipin Deep Kaur <vkaur@codeaurora.org>